A high voltage-high current transformer bushing having a cast resin insulating housing and hollow central conductor containing fluid coolant

ABSTRACT

A high voltage-high current bushing for connecting the output from an electrical generator to the primary or low potential winding of a step up transformer. The bushing comprises a hollow high current carrying member surrounded by insulating material having a ground shield embedded therein. The hollow high current carrying member contains liquid coolant material which increases the thermal time constant of the bushing and tends to eliminate hot spots in the current carrying member.

United States Patent f Kevin F. Friedrich Sharon, Pa.;

Richard D. Buckley, Athens, Ga. 5,179

Jan. 23, 1970 Aug. 31, 1971 Westinghouse Electric Corporation Pittsburgh, Pa.

Inventors Appl. No. Filed Patented Assignee U.S. Cl 174/15 BH, 174/31 R, 174/142, 174/152 R Int. Cl. ..H0lbl7l26, 11011) 17/54 Field of Search 174/1 1 BH,

12811, 14 BH, l5 BH, l6 BH, 18, 31 R, 142, 143, 152R,l53 R,l67

[56] References Cited UNITED STATES PATENTS 1,129,466 2/l9l5 Fortescue 1'74/15 (.3) X 1,526,023 2/1925 Steinberger 74/16 (.3) UX 2,809,358 10/1957 Whit ney 174/152 X 3,001,005 9/1961 Sonnenberg... 174/142 3,067,279 12/1962 Baker ..l74/15 (.3) UX 3,484,542 12/1969 Mathes et a1. 1'74/142 FOREIGN PATENTS 1,500 2/1932 Australia 174/142 823,812 11/1959 Great Britain 174/152 844,381 8/1960 Great Britain 174/15 (.3) 327,883 3/1958 Switzerland 174/143 Primary Examiner-Laramie E. Aslrin Alt0rneys-A. T. Stratton and F. E. Browder ABSTRACT: A high voltage-high current bushing for connecting the output from an electrical generator to the primary or low potential winding of a step up transformer. The bushing comprises a hollow high current carrying member surrounded by insulating material having a ground shield embedded therein. The hollow high current carrying member contains liquid coolant material which increases the thermal time constant of the bushing and tends to eliminate hot spots in the current carrying member.

PATENTEU AUBSI lsn 3.602.629

////l V/l 0nd Ric d D. Buc y ATTORNEY A'nrcnvocraciztmcncuimsurTR NSFO MER BUSHING nnvmcncssr nssm msumrmo HOUSINGAND n notirowcl-zu'ramicounucron conrnmmorwmcoomur BACKGROUNDOF-THEINVIENTION 1. Field of the Invention L This invention relates to hightvoltage-high current electrical/ bushings particularly'of the'type used for connecting 'th'e output from an electrical generator to the'primary' or input winding of a step up transformer.

2. Description of the Prior Art j v In the? prior art,'bushings usedforiconnectingthe output of an electricalgeneratorto thepl-imaryor input winding of a step-up transformerusually comprise a central conductor member surrounded by a porcelain insulator with gasketcd joints at each end of the porcelain insulator. This'type ofib'ush ing is satisfactorybut it'is expensive to manufacture'and hard to maintain in good workingiorderz Some reasons wh yfsuch a bushingrequires extensive maintenance-is because the purcelain members crack and 'the'gasketed' joints atthe e'nds" of the porcelain develop'lealts; Thisinvention eliminates the objections to the priorart bushings-byiprovidinga bushing which is simple to manufacture and easytomaihtain. Inthe bushing I sion line (not shown) for distribution to the customers. It is therefore seenlthatthe bushing 12 must function as a relatively high voltage bushing-which'carries high currents. The high of the present inventionthere are 'no'gasketed joints between;

the central conductor-andtheouterinsulating'coating. The coolant material is maintained in a central chamberfabricated with allwelded joints which lessens the possibilityofl'eaks' which occur in the prior 'art devices-having gasketed joints; The outerinsulatingcoating otlthe present invention is highly resistant'to cracks.

SUMMARY=OF THE INVENTION provided to the shield 'fOrgroundingthe shield to the transformer casing: Walls are provided near th'e endsof thehollow current carrying member to provide a reservoir orchamb'erin side the hollow current carrying memberfor"retainingfli'q uid thermal cycling. A stress grading or ground shield 28 is cast into the insulating member 24-and the shield 2 8 is spaced from coolant. which increases the time constant and tends to" eliminate or lessen hot spots in:thecurrentcarrying mem-be rii Means are provided near each end. ofthe hollow current-car-' rying member, beyond the insulationb'ody portion, forconnecting electrical conductors to the hollow current carrying? member.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a perspective view, with parts broken away,.showing a bushing as provided by this invention connecting the output of an electrical generator to the input orprimary winding DESCRIPTION OFTHE'PREFERRE'D EMBODIMENT Like reference characters referto' like elements throughout the variousfigures of the drawings.

Referring in detail to FIG. I; this figure shows the environ FIG. 1 is apartially perspective view showing astep-up transformer l0 having bushings 12 as provided bythis invention mounted thereon. Although only one bushing ;12is shown in'FIG. l the transformer isequipped with three bushings l2 asprovided by this invention. FIG. 1 also illustrates an electrical generator '14, with the output from each phase of the i N generator connected to one of the bushings 12 on the transformer 10 through isolated phase duct 16. The output or high voltagefrom the transformer 10 is connected to atransmission line-through three high-voltage bushings l8. As'seen'in FIG. I

thelbushings l2 areprotected from weather by a cover 20.

The output from the electrical generator 14is usually in the order of 23,000 volts at 10,000 amperes or higher. This output is connected through the isolated phase duct 16 to the bushings l2'which are connected to the low voltage orprimarywinding of the step-up transformer 10. This voltage is stepped up by the transformer 10 and applied to a transmiscurrents carried by the bushing will necessarily cause high heating of the current carrying elements of the bushing. Because of thisheating, sufficient means must be built into the bushing to handle this high heat without damaging the bushing and the associated transformer.

Referring to FIG. 2;which shows a longitudinal sectional view of the bushing 12 provided by this invention, it is seen that the bushing l2provided by this invention comprises a :Iarge cross se'ction'curren't carrying'niember 21. This current.

carrying member 21 may be rectangular, square. circular or triangular -in cross section and is made from'an aluminum extrusion. However it is understood that any other type of good current conducting metal and any other hollow cross section could be'used for making the current carrying member '21. In one common size bushing the current carrying'member'2l is approximately 10 inches square and approximately 44 inches long. The current carrying member 21 has a serrated or rough portion 22 provided thereon near its upper end. The remainder of the lengthof the current carrying member is coated with a mold release material 23-and a resin insulator 24 is cast'onto thecurrent carrying member The serrated or roughened portion 22 of the current carrying member firmly bonds with'the cast insulatingmember 245 however, the mold release material 23f'over the remaining. portion of 'thecurrent carrying'm'ember permits the current carrying member to movewith'respect to the resin insulating member 24 over i mostof the length" of the current carrying member 21 when the current carrying member 21 expands or contracts due to the current carrying member 21. The shield 28 is connected byrn'eansof a conductor 30 to an insert 32 for grounding the tend beyond the ends of the insulating member 24. The ends normally be used.

36'and 38 are providedwith a plurality of holes 40 which are used "to attach leads 50 from the generator to the bushing by means of bolts 42 and nuts 44 and to connect the low-voltage winding of the transformer 10' to the lower end of the bushing by means of lead 51 and bolts 46 and nuts'48. A plurality'of holes 4'0may be provided on all four sides of the rectangular current carrying member 21 at each end thereof to provide for the convenience of attaching leads such as 50 or 51 to any of the four sides of the current carrying member 20. This conveni'ence of connection is often important since it facilitates easy connection of the heavy stiff leads 50 and 51 to the current carrying member 21 regardless of the direction from which" the leads 50 and SI approach the current carrying member 21.

- The terminal portions 36 and 38 of the current carrying member 21' are coated with a good tin-silver or other good low-resistance electrical connection between the leads 50 and 51 and the current carrying member21.

The bushing 12 is attached to the top wall 34 of the transformer by means of a plurality of bolts such as 56, which extend through bolt holes 58 in the flange portion 59 of the bushing 12 and engage threaded holes 60 in the tank wall 34. As indicated in FIG. l metallic inserts 32 are provided inthe flange portion 54 of the bushing which receives the bolts 56 to provide ground connection between the ground shield 28 and the top wall 34 of the transformer 10.

A fluid tight seal is provided between the flange portion 59 of the bushing 12 and the tank wall 34 by means of a gasket 61 which is clamped tightly between the wall 34 of the transformer 10 and the flange portion 59 of the bushing 12 when the bushing is mounted on the wall 34 of the transformer 10.

The upper end of the hollow rectangular current carrying member 21 is closed by a metallic plate 62. The plate 62 is welded, brazed or otherwise joined to the inside walls of the current carrying member 21 to provide a fluid tight connection between the plate 62 and the four sidewalls of the current carrying member 21. Likewise a wall member 64 isprovided near the lower end of the current carrying member 21 to provide a fluid tight connection with the four sidewalls of the current carrying member 21. Each of the walls 62 and 64 is provided with a removable screw threaded plug 66. The chamber or compartment provided by the walls 62 and 64 is filled with a good coolant material to increase the thermal time constant of the bushing and to reduce the hot spot temperature of the current carrying member 21. The removable plugs 66 facilitate draining and filling of the compartment 68 provided by the walls 62 and 64 and the sidewalls of the current carrying member 21 with a good grade of fluid coolant 70, such as mineral oil or the like.

A plurality of weather sheds 72 are cast or molded into the insulating member 24 when the insulating member 24 is cast or molded about the current carrying member 21.

FIG. 3 is a top view of the insulator shown in longitudinal sectional view in FIG. 2.

The bushing provided by this invention comprises a substantial improvement over the bushings of the prior art for connccting the output from a high voltage-high current electrical generator to the primary or low-voltage winding of a step-up transformer. The bushing is of substantially lower cost than the prior art bushings and the simple construction of the bushing requires less maintenance than the prior art bushings. A typical bushing constructed according to the teachings of this invention requires approximately 300 pounds of resin to form the insulating portion 24, pounds of aluminum to provide the current carrying member 21, 10 pounds of aluminum to provide the shield 28, and approximately pounds, or 13 gallons of coolant to fill the compartment 68; therefore, the bushing 12 filled with dielectric totals approximately 5 l0 pounds of material. I

It is also seen that because of the large area of the current carrying member 21 in a bushing of this type that the deleterious effects of heating by'the high currents carried by the bushing may be maintained at a minimum.

- We claim as our invention:

l. A high-current bushing comprising an elongated hollow metallic current carrying member having four sidewalls and first and second ends, resininsulating material cast around said current carrying member, said resin insulating material terminating short of said first and second ends of said current carrying member, shield means cast in said resin insulating material in spaced relationship to said current carrying member, terminal means connected to said shield means, said cast resin insulating material comprising a flange for mounting said bushing, a pair of substantially transverse wall members weldedinside said hollow current carrying member with a fluid tight joint, said transverse wall members being spaced from each other with a substantially transverse wall member adjacent each of said first and second ends of said current carrying member, said pairpf substantially transverse wall members providing a liquid tight chamber between said transverse 

1. A high-current bushing comprising an elongated hollow metallic current carrying member having four sidewalls and first and second ends, resin insulating material cast around said current carrying member, said resin insulating material terminating short of said first and second ends of said current carrying member, shield means cast in said resin insulating material in spaced relationship to said current carrying member, terminal means connected to said shield means, said cast resin insulating material comprising a flange for mounting said bushing, a pair of substantially transverse wall members welded inside said hollow current carrying member with a fluid tight joint, said transverse wall members being spaced from each other with a substantially transverse wall member adjacent each of said first and second ends of said current carrying member, said pair of substantially transverse wall members providing a liquid tight chamber between said transverse wall members for retaining coolant inside said elongated hollow metallic current carrying member, and terminal means located on the sidewalls of the respective ends of said current carrying member which extend beyond said resin insulating material adjacent the ends of said current carrying member for connecting electrical conductors to the sidewalls of said current carrying member. 